1. Field of the Invention
The present invention relates to a thin film magnetic head having at least an inductive-type magnetic transducer for writing and a method of manufacturing the same.
2. Description of the Related Art
In recent years, performance improvement in thin film magnetic heads has been sought in accordance with an increase in surface recording density of a hard disk drive. A composite thin film magnetic head, which is made of a layered structure having a recording head with an inductive-type magnetic transducer for writing and a reproducing head with a magneto resistive element (referred to as MR element in the followings) for reading-out has been widely used as a thin film magnetic head. As MR elements, there are an AMR element that utilizes the anisotropic magnetoresistive effect (referred to as AMR effect in the followings) and a GMR element that utilizes the giant magnetoresistive (referred to as GMR effect in the followings). A reproducing head using the AMR element is called an AMR head or simply an MR head. A reproducing head using the GMR element is called a GMR head. The AMR head is used as a reproducing head whose surface recording density is more than 1 gigabit per square inch. The GMR head is used as a reproducing head whose surface recording density is more than 3 gigabit per square inch.
In general, an AMR film is made of a magnetic substance that exhibits the MR effect and has a single-layered structure. In contrast, many of the GMR films have a multi-layered structure consisting of a plurality of films. There are several types of producing mechanisms of the GMR effect. The layer structure of a GMR film depends on the mechanism. The GMR films include a super lattice GMR film, a spin valve film, a granular film and so on. The spin valve film is most efficient as the GMR film which has a relatively simple structure, exhibits a great change in resistance in a low magnetic field, and is suitable for mass reproducing.
As a primary factor for determining the performance of a reproducing head, there is a pattern width, especially an MR height. The MR height is the length (height) between the end of an MR element closer to an air bearing surface and the other end. The MR height is originally controlled by the amount of grinding when the air bearing surface is processed. The air bearing surface (ABS) is a surface of a thin film magnetic head facing a magnetic recording medium and is also called a track surface.
Performance improvement in a recording head has also been expected in accordance with the performance improvement in a reproducing head. It is necessary to increase the track density of a magnetic recording medium in order to increase the recording density among the performance of a recording head. In order to achieve this, it is necessary to develop a recording head with a narrow track structure, the width of a bottom pole and a top pole sandwiching a write gap on the air bearing surface being reduced to the order of some microns to submicron. Semiconductor process technique is used to achieve the narrow track structure.
Another factor determining the performance of a recording head is the throat height (TH). The throat height is the length (height) of a portion (magnetic pole portion) from the air bearing surface to an edge of an insulating layer which electrically isolates the thin film coil. Reducing the throat height is desired in order to improve the performance of a recording head. The throat height is also controlled by the amount of polishing when the air bearing surface is processed.
In order to improve the performance of a thin film magnetic head, it is important to form the recording head and the reproducing head in well balance.
Here, an example of a method of manufacturing a composite thin film magnetic head as an example of a thin film magnetic head of the related art will be described with reference to FIGS. 10A and 10B to FIGS. 15A and 15B.
As shown in FIGS. 10A and 10B, an insulating layer 102 made of, for example, alumina (aluminum oxide, Al2O3) is formed in a thickness of about 5 to 10 μm on a substrate 101 made of, for example, altic (Al2O3.TiC). Then, a bottom shield layer 103 for a reproducing head made of, for example, permalloy (NiFe) is formed on the insulating layer 102.
Next, as shown in FIGS. 11A and 11B, for example, alumina of about 100–200 nm in thickness is deposited on the bottom shield layer 103 to form a shield gap film 104. Then, an MR film 105 of tens of nanometers in thickness for making up the MR element for reproducing is formed on the shield gap film 104, and photolithography with high precision is applied to obtain a desired shape. Next, a lead terminal layer 106 for the MR film 105 is formed by lift-off method. Next, a shield gap film 107 is formed on the shield gap film 104, the MR film 105 and the lead terminal layer 106, and the MR film 105 and the lead terminal layer 106 are buried in the shield gap films 104 and 107. Then, a top shield-cum-bottom pole (called bottom pole in the followings) 108 of about 3 μm in thickness made of, for example, permalloy (NiFe), which is a material used for both the reproducing head and the recording head, is formed on the shield gap film 107.
Next, as shown in FIGS. 12A and 12B, a write gap layer 109 of about 200 nm in thickness made of an insulating layer such as an alumina film is formed on the bottom pole 108. Further, an opening 109a for connecting the top pole and the bottom pole is formed through patterning the write gap layer 109 by photolithography. Next, a pole tip 110 is formed of magnetic materials made of permalloy (NiFe) and nitride ferrous (FeN) through plating method, while a connecting portion pattern 110a for connecting the top pole to the bottom pole is formed. The bottom pole 108 and a top pole layer 116 which is to be described later are connected by the connecting portion pattern 110a and so that forming a through hole after CMP (Chemical and Mechanical Polishing) procedure, which is to be described later, becomes easier.
Next, as shown in FIGS. 13A and 13B, the write gap layer 109 and the bottom pole 108 are etched about 0.3–0.5 μm by ion milling having the pole tip 110 as a mask. By etching to the bottom pole 108, a trim structure is formed. As a result, widening of effective write track width can be avoided (that is, suppressing spread of magnetic flux in the bottom pole when data is being written.) Then, after an insulating layer 111 of about 3 μm, made of, for example, alumina is formed all over the surface, the whole surface is planarized by CMP.
Next, as shown in FIGS. 14A and 14B, a thin film coil 112 for an inductive-type recording head made of, for example, copper (Cu) is selectively formed on the insulating layer 111 by, for example, plating method. Further, a photoresist film 113 is formed in a desired pattern on the insulating layer 111 and the thin film coil 112 by photolithography with high precision. Then, a heat treatment of a predetermined temperature is applied to planarize the photoresist film 113 and to insulate between the turns of the thin film coils 112. Likewise, a thin film coil 114 and a photoresist film 115 are formed on the photoresist film 113, and a heat treatment of a predetermined temperature is applied to planarize the photoresist film 115 and to insulate between the turns of the thin film coils 114.
Next, as shown in FIGS. 15A and 15B, a top pole yoke-cum-top pole layer (called a top pole layer in the followings) 116 made of, for example, permalloy, which is a magnetic material for recording heads, is formed on the top pole 110, the photoresist films 113 and 115. The top pole layer 116 is in contact with the bottom pole 108 in a rearward position of the thin film coils 112 and 114, while being magnetically coupled to the bottom pole 108. Then, an overcoat layer 117 made of, for example, alumina is formed on the top pole layer 116. At last, a track surface (air bearing surface) 118 of the recording heads and the reproducing heads is formed through a slider machine processing, and a thin film magnetic head is completed.
In FIGS. 15A and 15B, TH represents the throat height and MR-H represents the MR height, respectively. P2W represents the track (magnetic pole) width.
As an factor for determining the performance of a thin film magnetic head, there is an apex angle as represented by θ in FIG. 15A besides the throat height TH and the MR height MR-H and so on. The apex angle is an angle between a line connecting the corner of a side surface of the track surface of the photoresist films 113 and 115, and an upper surface of the top pole layer 116.
To improve the performance of a thin film magnetic head, it is important to form the throat height TH, the MR height MR-H, the apex angle θ, and the track width P2W as shown in FIGS. 15A and 15B precisely.
Especially in recent years, to enable high surface density recording, that is, to form a recording head with a narrow track structure, submicron measurement of equal to or less than 1.0 μm is required for the track width PW2. Therefore, a technique of processing the top pole to submicron using a semiconductor processing technique is required. Also, using the magnetic materials having higher saturation magnetic flux density for the magnetic pole is desired in accordance with being a narrow track structure.
The problem is that it is difficult to minutely form the top pole layer 116 on a coil area (apex area) being protruded like a mountain covered with photoresist films (for example, the photoresist films 113, 115 shown in FIG. 15A.)
As a method of forming the top pole, the frame plating method, as disclosed in, for example, Japanese Patent Application laid-open in Hei 7-262519, is used. When the top pole is formed by the frame plating method, first, a thin electrode film made of, for example, permalloy is formed all over the apex area. Next, photoresist is applied on the apex area, and by patterning it through photolithography, a frame for plating is formed. Then, the top pole is formed through plating using the electrode film formed earlier as a seed layer.
There is, for example, equal to or more than 7 to 10 μm differences in height in the apex area. If the film thickness of the photoresist formed on the apex area is required to be equal to or more than 3 μm, a photoresist film of equal to or more than 8 to 10 μm in thickness is formed in the lower part of the apex area since the photoresist with liquidity gathers into a lower area. To form a narrow track as described, a pattern with submicron width is required to be formed with a photoresist film. Accordingly, it is necessary to form a micro pattern with submicron width with a photoresist film of equal to or more than 8 to 10 μm in thickness, however, it has been extremely difficult.
Moreover, during an exposure of photolithography, a light for the exposure reflects by an electrode film made of, for example, permalloy, and the photoresist is exposed also by the reflecting light causing deformation of the photoresist pattern. As a result, the top pole can not be formed in a desired shape because side walls of the top pole take a rounded shape and so on. As described, with a related art, it has been extremely difficult to precisely control the track P2W and to precisely form the top pole so as to have a narrow track structure.
For the reasons described above, as shown in the procedure of an example of the related art in FIGS. 12A and 12B–15A and 15B, a method of connecting the pole tip 110 and a yoke-cum-top pole layer 116 after forming a track width of equal to or less than 1.0 μum with the pole tip 110 which is effective for forming a narrow track of a recording head, that is, a method of dividing the regular top pole into the pole tip 110 for determining the track width and the top pole layer 116 which becomes the yoke area for inducing magnetic flux is employed (Ref. Japanese Patent Application laid-open Sho 62-245509, and Sho 60-10409). By dividing the top pole into two as described, the pole tip 110 can be minutely processed to submicron width on a flat surface of the write gap layer 109.
However, there have still existed problems as follows regarding the thin film magnetic head.                (1) First, in a magnetic head of the related art, the throat height is determined in the end of a further side from the track surface 118 of the pole tip 110. However, if the width of the pole tip 110 becomes narrower, the pattern edge is formed in a round shape by photolithography. Therefore, the throat height, which is required to have a highly precise measurement, is not formed to be uniform. As a result, the track width of the magnetoresistive element becomes unbalanced in a procedure of processing and polishing of the track surface. For example, if the track width with 0.5–0.6 μm is required, the end of a further side from the track surface 118 of the pole tip 110 shifts from the throat height zero position to the track surface side and writing gap is widely opened. As a result, the problem that writing of recording data cannot be performed has often occurred.        (2) As described above, in the magnetic head of the related art, it is not necessary to process the top pole layer 116 as minute as the pole tip 110, because the track width of the recording head is determined by the pole tip 110 which is one of the top pole being divided into two. However, since the position of the top pole layer 116 is determined in the upper area of the pole tip 110 by positioning of photolithography, if both of the top pole layer 116 and the pole tip 110 are largely shifted to one side when looking at the structure from the track surface 118 (FIG. 15A) side, so-called side write for performing writing on the top pole layer 116 side occurs. As a result, the effective track width becomes wider and writing is performed in a region other than the designated data recording region in a hard disk.        
Further, if the track width of the recording head becomes extremely minute, especially equal to or less than 0.5 μm, the process precision of submicron width is required in the top pole layer 116. That is, if the measurement difference in the lateral direction of the pole tip 110 and the top pole layer 116 is too significant when looking at them from the track surface 118 (FIG. 15A) side, as described above, a side write occurs. As a result, writing is performed in a region other than the originally designated data recording region in a hard disk occurs.
Accordingly, not only the pole tip 110 but also the top pole layer 116 is required to be processed to the submicron width. However, it is difficult to perform fine-process of the top pole layer 116 since there is a significant difference in height as described above in the apex area under the top pole layer 116.                (3) In the magnetic head of the related art, there is a problem that it is difficult to shorten a yoke length. That is, the narrower the coil pitch becomes, the easier the achievement of a head with short yoke length becomes and, especially, a recording head with a high frequency characteristics can be formed. However, when the coil pitch is made indefinitely small, the distance from the throat height zero position to the outer periphery end of the coil becomes a main factor for preventing the yoke length from shortening. The yoke length can be made shorter with two-layered coil than one-layered coil so that many of the recording heads for high frequency employ the two-layered coil.        
In the magnetic head of the related art, after forming a first layer of coil, a photoresist film of about 2 μm thick is formed in order to form an insulating film between the turns of the coils. Therefore, a small apex area having a rounded shape is formed in the outer peripheral end of the first layer of the coil. Next, a second layer of the coil is to be formed thereon. However, etching a seed layer for forming the second layer can not be performed in the slope of the apex area causing the coil to short-circuit, which makes it impossible to form the second layer of the coil. Accordingly, the second layer of the coil is required to be formed on a flat area. When the slope of the apex area is 45–55°, if the thickness of the coil is 2–3 μm and the thickness of the insulating film between the turns of the coil is 2 μm, the distance from the outer peripheral end of the coil to the vicinity of the throat height zero position is required to be 6–8 μm which is twice of 3–4 μm, (the distance from the contact area of the top pole and the bottom pole to the outer peripheral end of the coil is also required to be 4–5 μm). This has been the main factor for preventing the yoke length from shortening. For example, when forming two layers of coils with 11 turns with line/space being 1.5 μm/0.5 μm, suppose the first layer is 6 turns and the second layer is 5 turns, then the length of the coil of the yoke length is 11 μm. Therefore, since 6–8 μm is required in the apex area of the outer peripheral end, shortening of the yoke length is impossible. This has prevented the high frequency characteristics from improving.
Further, as the throat height of each thin film coil is close to the zero position, a magnetomotive force can be conducted more into the top pole and the thin film magnetic head with excellent recording characteristic can be achieved. Accordingly, the throat height of the thin film coil is desirably as close to the zero position as possible.
Related arts for shortening the yoke length include those disclosed in Japanese Patent Application laid-open Hei 6-176318 and Hei 5-120628. The Japanese Patent Application laid-open Hei 6-176318 discloses a technique in which a space width between the turns of the coils is reduced to form a multi-layer coil with high density and low resistance and, in order to shorten the yoke length, after forming the first coil, an insulating layer is formed between the turns of the first coils to form a thick second coil on the first coil by using the insulating layer as a mask. However, in this technique, it is not possible to form a thin film coil in the vicinity of the throat height zero position and to conduct a magnetomotive force from a thin film coil to a pole efficiently. Further, the problems described above, including precision control of the throat height at the recording head, can not be solved. On the other hand, in the Japanese Patent Application laid-open Hei 5-120628, in the area where a conductive coil is formed, a first metal layer compositing a gap layer is placed at the bottom side of the conductive coil, and an insulating layer and a second metal layer are placed at the upper side of the conductive coil in order to shorten the yoke length. However, in this technique, it is not possible to conduct the magnetomotive force from a thin film coil to a pole efficiently, and the problems described above, including precision control of the throat height, can not be solved.
The invention is presented to solve these problems. The first object is to provide a thin film magnetic head in which a magnetomotive force from the thin film coil can be conducted to a pole efficiently and improve a recording characteristic in the recording head, and a method of manufacturing the same.
The second object is to provide a thin film magnetic head which can precisely control a throat height in the recording head and in which a yoke length is shortened so that a magnetomotive force from the thin film coil can be conducted to a pole efficiently to improve the high frequency characteristic and the recording surface density, and a method of manufacturing the same.
The third object is, in addition to the effects described above, to provide a thin film magnetic head in which the submicron width of the top pole layer can be minutely processed and, further, whose characteristic of the recording head can be improved, and a method of manufacturing the same.